MycoBank number:MB 81049;Index Fungorum number:IF 81049;Facesoffungi number: FoF 03134, 89 species.

Saprobicon wood, bark, resin, cones, scales, needles, seeds, and roots of gymnosperms, much less frequently on angiosperms. Predominantly temperate in distribution.Sexual morph:Ascomatasuperficial, scattered to gregarious, black, sometimes less connivent, more appressed, hysterioid, grouped in triangular or radiating star-shaped or astral arrangement, fragile, yet persistent, carbonaceous, globoid to obovoid, to strongly laterally compressed erect, bivalve shell- shaped structures, standing on edge, with lateral walls more or less connivent, and extended vertically to a prominent longitudinal keel or cristate apex; distinctly clam- or musselshaped.Peridiumfragile, thin-walled, scleroparenchymatous, rarely of multiple layers.Hamatheciumcomprising narrow trabeculate pseudoparaphyses, borne gelatinous matrix, often sparse to lacking at maturity.Asci8-spored, rarely 4-spored, bitunicate, fissitunicate, cylindrical, with a broad, short pedicel, ocular chamber not well developed, borne on a basal cushion, centrally orientated within the centrum, rarely borne laterally.Ascosporesoverlapping 1–2-seriate or in one or two fascicles within the ascus, hyaline to pigmented yellow to dark brown, highly variable in septation, showing bipolar symmetry.Asexual morph: Primarily coelomycetous or less frequently hyphomycetous (Lohman 1932, 1933a, b, Blackwell & Gilbertson 1985, Speer 1986).

Type –MytilinidionDuby,

Notes – The generaMytilinidion,LophiumandQuasiconchaformed a monophyletic clade, representing Mytilinidiales (Boehm et al. 2009b). The conchate nature of the hysterothecia and the thin-walled peridium are characteristic features of this group (Boehm et al. 2009a, b, Hyde et al. 2013). Although, Boehm et al. (2009a) and Hyde et al. (2013) mentioned thatMytilinidiaceaehave trabeculate pseudoparaphyses,Mytilinidion didymosporaintroduced by Jayasiri et al. (2018) has cellular-like pseudoparaphyses (see Jayasiri 2018 Fig. 14). Several species ofMytilinidiaceaewere shown without clear pictures of hamathecium, thus we suggest that morphological study of hamathecium is needed for future works.

Our multi-gene phylogenetic analysis confirms the placement of Mytilinidiales within the class Dothideomycetes. Gloniales is introduced in this study based on their diverse morphology. Therefore, the Mytilinidiales is a monotypic order withMytilinidiaceae.

Species